Clock writer for magnetic data storage devices



Jul? 20, 1965 A. c. FRANcols 3,196,420

CLOCK WRITER FOR MAGNETIC DATA STORAGE DEVICES Filed Jan. 29. 1962United States Patent O 3,196,420 CLOCK WRITER FR MAGNETlC DATA STRAGEDEVICES Alex C. Francois, Farmington, Mich., assigner to Ex-Cell-OCorporation, Detroit, Mich., a corporation of Michigan Filed Jan. 29,1962, Ser. No. 169,404 Claims. (Cl. S40-174.1)

The present invention relates to clock writer for magnetic storagedevices in general and more particularly to means yfor placingsynchronization pulses, sometimes also called timing or sprocket pulses,upon a closed loop clock track on the recording medium of a magneticdisc or drum.

It is well known that data recorded on magnetic data `storage apparatusmust be recorded and read in synchronization with timing pulses, inorder to insure perfect synchronism between the recording on and readingfrom the record medium and the general operation of the equipment, suchas a computer 4for example, which is associated .with the magnetic datastorage apparatus. Consequently, at least one clock track is permanentlyrecorded, for the above mentioned purpose, in a closed loop upon themagnetizable surface of the data storage apparatus, -be it in the formof a disc or a drum.

The clock track consists of a series of magnetic pulses of a givenfrequency that must rem-ain accurately constant all around the track andwhich must form a perfectly closed loop without break o-r lapse in thecontinuous train of pulses, with the first pulse of the loop and thelast pulse of the loop joined accurately Without mismatching of theirrespective phases in order to provide a loop without `beginning nor end.An exact number of pulses must therefore be recorded on a track of agiven length and no foolproof method has hitherto been devised ytoimpress upon a closed track on a disc or a drum a perfectsynchronization pulse train of a given frequency. It is obvi-ous that ifthe pulse train is supplied -by a pilot generator furnishing even aperfectly stable pulse frequency, means must be provided to insure thatthe disc or drum is rotating at a constant velocity during at least onerevolution while the clock track is being recorded. Furthermore theproblem remains of causing the last and first pulses in the loop tomerge in a way which is indistinguishable from the Way in which all theother pulses are associated. It is also obvious that great difficultiesexist where it is desired to record a given number of pulses, each oneof which occupy an infinitesimal length on the track, in a circle thelength of which cannot be determined with any degree of precision bymeans lmown today.

It is evident that the important factor in establishing asynchronization track is to be able to record a given number of pulsesin a complete clock track. The actual frequency of the pulse train, inrelation to exact time, is immaterial as the frequency will vary withvariations in the angular velocity of the disc or drum supporting theclock track. However, because the data is being recorded Von or readfrom tracks rotating in unison with the clock track, perfect relativetiming and synchronization of the information pulses with the clockpulses will exist at all times due to the data recording or readingoperation being effected under the control of the clock pulses.

The present invention teaches a method of recording a clock track on adisc or a drum in a simple manner which nevertheless insures that aperfect track will be recorded at all times.

One object of the invention, therefore, is to provide an improved clockwriter for magnetic data storage apparatus of the disc or drum types.

Another object of the invention is to provide means 3,136,420 PatentedJuly 20, 1965 ICC for recording a clock track of a given frequencycontaining an exact number of timing pulses per revolution -of the discor drum.

Another object of the invention is to effectuate the recording of timingpulses on a clock track in synchronization with the rotation of the discor drum on which the clock track is being recorded.

A further object of the invention is to provide means for building up apulse train of a given period into a provisory loop and for manuallyVarying the period preparatoly to recording the pulse train into adefinitive clock trac Yet another object of the invention is to utilizethe rotation of the disc or drum to generate the pulse train and totrigger the beginning .and the end of the recording of the clock track.

Yet a further object of the invention is to generate the pulse train andeffectuate the recording of the clock track in perfect synchronizationwith the rotation of the disc or drum. Other objects and advantages willbecome apparent from the following description with reference to theaccompanying drawing illustrating, in a block diagram form, theprinciple of a clock writer according to the invention.

A drum or disc 1 is shown arbitrarily as having, inter alia, the threetracks identified by T1, T2 and T3. It is to be understood that T1, T2and T3 are preferably three concentric tracks on the same face of amagnetic disc `or three parallel tracks anywhere on the peripheralsurface of a magnetic drum. Alternately, T1, T2, T3 may be situated onseparate discs keyed or otherwise fastened, provisorily or permanentlyon a common spindle for rotation in unison, or on any combination `ofdiscs and drums on a common driving spindle. This synchronized rotationyof tracks T1, T2 and T3 is schematically represented by the dot anddash line passing through the centers of the circles representing tracksT1, T2 and T3.

On the same shaft, and in synchronized rotation with the support oftracks T1, T2 and T3, is mounted a tachometer 3 supplying a pulse foreach revolution of the shaft, which pulse is read by a read head 4.

This pulse is fed to an amplifier 5 when a switch operated by pushbutton 6 is closed. The output from amplifier 5 is fed through an ORgate 7 to a Write amplifier, designated by numeral 8, which is in turnconnected to write head 9 adapted to record on track T1, A read head 10is disposed at a fixed angular distance D1 from write head 9. An erasehead 11 is positi-oned after the read head lti.

The output of the OR gate 7 is also connected to another writeamplifier, designated by numeral 12, hav-ing its output connected towrite head 13, adapted to write on the second track T2. A read head 14,adapted to read track T2, is angularly positioned at distance D2 fromthe Write -head 13. Erase head 15 is mounted a short distance beyond theread head 14. The read head 14 is movable along track T2, and itsangular position D2 relatively to its corresponding write head 13 islarger or smaller than D1, the angular position of read head 10relatively to the Write head 9 on track T1. D2 is here larger than D1,Ibut it is to be understood that the operation of the invention would beidentical in the event that D2 had been arbitrarily chosen as smallerthan D1, as the all irnportant factor is that DZ and D1 be not equal.

By depressing push button 6, a single tachometer pul-se is recordedsimultaneously on both tracks T1 and T2. The clockwise rotation of thedisc or drum, as indicated by the arrows, brings the pulse recorded ontrack T1 under the read head 10 before the pulse recorded on track T2arrives under the read head 14. The spacing between the two pulses isD2eD1. The first pulse is read by read head 10 and, after beingamplified by read ampliier16, is'fed through the'OR gates 17 and'7'tothe Ywrite amplifiers 8 and 12. That rst pulse is re-recorded tracks T1and T2 as explained hereinbefore.A `The sec- 'ond pulse isthen -read bythe read head `10, and consequently recordedon the two tracks at thesame time as 'the rst 'pulseonftrack T2 isread by the read head 1,4,resulting in only one pulse being re-recorded simul-V taneously onboth'tracks.' Shortlythereaffterthe second pulse on track T2 is read byread head 14.and is also re-recorded simultaneously on both tracks. Bothtracks 'have now three rfc-recorded pulses. VThe previouslyfre- 'cordedpulses are continuously erased lon both tracks"- Vduring their passingunder the erase heads, in order Vto '1 clear the tracks vpreparatorilyVto 1re-recording of theY "pulses, .y

continues for each revolution Vof the disc or drum with an addition ofoneA pulse per revolution until This action a complete pulsetrain isbuilt in each, ofthe loopsof tracks T1 and T2V represented by the'segments off said tracks comprised between write head 9 and read head`10, and between write head 13and Vread head 14grespectively. Thepulsetrains are continuously regenerated; by being continuouslyre-recorded on the tracks, and the clock track at a nominal frequency of150 kilocycles for Va rotation velocity of the disc or drum of l900rpm.,

simultaneous pulse trains are built up in track T1 and T2 ashereinbeforeexplained. The period of the pulses is P:DZ-Dl and thenumber of pulses available for recording' on clock track T3 during onerevolution of the disc or drum is indicated by the counter 20. Themovable head 14 isadjusted until'the counterindicates that exactly10,000 pulses per revolution of the disc or drum are available forrecordingon the clock track.y The pushbuttonk 23 is then depressedftoinitiate the recording on track T3, as explained hereinbeiore, and10,000 pulses 'are recorded ionfclocktrack T3, forming a'completeclosed-loop thereon.- f y The nominal velocity of the disc or drum'being 900 rpm. or 15 revolutions per second, the nominal frequency of-thepulses yon the clock track is 10,000 15 or 150,000 cycles persecond.

It is" obvious that anyone skilled in the art possesses Vsuflicientknowledge, enabling him to construct or purchase the commerciallyavailable components indicated in the accompanyingyblock diagram andreferred to in this `specification as vwrite,amplifier, read amplifier,OR 'and AND gates, etc.','.a'nd'tl1ose components which, per se, arewell known Yin the art are not herein illustrated 'nor described indetail, furthe sake .of simplifying the description of the invention.-

It is to be understood that the above-described yarrangement is'v onlyillustrative ofthe present invention and that period ofthepulsesisPf-DZ-Dl. Their fundamental frequency proportional tofthe discordrum rotational speed. The total number of .pulses in each loopis equalThe pulsesare also Vfed through the OR gate and anAND gate 19 to acounter 20, which may be a binary counter capable of giving arvisu'alindication ofthe` number of -pulses counted in a certain period*of'time; TheV v AND'gate 19 is controlled by the tachometer pulse andfrom the tachometer'3. This number is Vthe numberV ot vpulses availablefor recording o nfthe clock track.- An

oscilloscope 22,v having ,its time basis synchronized by thetachometerpulses,imay be used, if so desired, vto obi i vThe movableread head14 is serve the pulse train. adjusted until the numbeuof pulseswhich is desired to be recorded on the clock track shows constantlyv onthe.r

counter and until Vthe representation of the pulse'train eofff on thescope stops drifting; 'Push-' button 23'-isthen de- ,I

pressed to trigger a ,single cycle,V gate 24whi'chain'turn' enables anAND gatevZS, andthe pulsetrain is-recorded on the clock track'TS of thedisc or drum by means of Vwrite amplifier 26 and -Write head 27. T henext tachorneter. pulse fed tothe single cycle gate24rcauses it rtodis'-v able the AND gate 25 as soongas the-disc lor drum hasaccomplished one .'revolution. 1 A clockfor sprocket track "has now beenrecorded on the disc'or drumat the desired frequency' and inperfectsynchronization with the; revolution'of the disc or drum,yresulting'in acomplete `con' f ti'nuous closed loop of pulses beingrecordedion the clock Y i track. I Variations in the revolutionvrvelocity of thereord medium have no influence on the quality of theclock track as it `can be seen that the pulses are being generated,

' regenerated, recirculated and recorded on the clock track T3 inperfect synchronismwiththe rotationV of the record medium.

Assuming that vit is desiredV for example to record a numerous othervariations and arrangements may be devviserl by those skilledin thea'rtWithout departing from fthe1 spirit and scopenof the invention.

What is claimed as new is;

1. Apparatus for'generating and Vrecording synchroni- ,zation pulses onlthe clock trackI o fa rotatable, record medium forrnir1g-y part of amagneticr data vstorage device,

said apparatus comprising:

Vmeans generating one pulse per revolution of said rec- Ordmedum; i

recording meansfrecording one such pulse simultaneouslyjon'a tirst andaseeonditrack adapted for concomitant rotation with said recordmedium;rst means reading said pulse from rsaid iirst track for re-recording ofsaid pulse by said recording means v as a rst pulse simultaneously onsaid first and second tracks; f. Y second means reading said pulsefromsaid second track for re-recording of said pulse bysaid recording meansas a second pulse simultaneously on said rst'and secondtracks, theperiod between said rstand second pulse being-.proportional to theangular distance y Y between said first ,and second means;

said' recordingV means re-reeording the pulses read yby said rst and'second Vmeans, adding one more pulse Ion bothlfirst and second tracksfor ea'ch revolution of said record medium until complete pulse trainsare continuously recirculating in the loops of said rst and secondtracks;

separate meanspositioned respectlvely after said first and second meansfor "erasing pulses from said rst and second tracks preparatorily tore-recording Asaid pulses', f f

means triggered by each revolution ofV said record medium Vfor counting`and displaying pulses available for each said revolution;

' means manually adjustingthefperiod of said'pulses un- Y .til the meanscounting said pulses display a con.- Y Vstant and `predetermined numberof said pulses;

' and .controllable means for recording said pulses on the clock trackonsaid record medium, the beginning and the end of the recording'cyclebeing timed between `a iirst and a secondfpulse `generated by said rstmentioned means.

2. The apparatusof claim lfwhereinV the means generating one pulse perrevolution of said record medium is a tachometer in synchronizedrotation with said record medium.

3. The apparatus of claim 2 wherein said rst and second tracks are on aseparate record medium provisorily mounted on a common shaft with saidrecord medium for simultaneous rotation therewith.

4. Apparatus for generating and recording synchronization pulses on atrack of a rotatable record medium, said apparatus comprising:

means generating one pulse per revolution of said rec-V ord medium;

means utilizing one such pulse for building up a continuouslyregenerative closed loop of equally spaced pulses;

means manually adjusting the period of the pulses in said loop;

means counting and displaying the number of pulses available within onerevolution of said record medium;

and controllable means triggered during one revolution of said recordmedium for transferring a continous train of pulses from said closedloop to a track on said record medium.

5. The apparatus of claim 4 wherein the means utilizing one of thepulses available at each revolution of the record medium for building upa continuously regenerative closed loop of equally spaced pulsescomprises:

separate recording means recording said pulse simultaneously on twoseparate tracks;

reading means on one track at an angular distance D1 from itscorresponding recording means for reading said pulse and re-recordingsaid pulse simultaneously on both tracks Via said recording means;

reading means on the other track at an angular distance D2 from itscorresponding recording means for `reading said pulse and re-recordingsaid pulse simultaneously on both tracks;

thereby causing two pulses separated 'by an angular distance D2-D1 to`be recorded on both tracks after one revolution of said record medium;

and causing n pulses to be recorded on both tracks after n revolutionsof said record medium;

whereby said n pulses form a continuously recirculating loop betweensaid reading and recording means on both tracks.

References Cited bythe Examiner UNITED STATES PATENTS 2,801,407 7/57Lubkin S40- 174.1 2,832,064 4/58 Lubkin 340-l74.1 2,903,677 9/59 Curtis340-174.1 2,926,341 2/ 60 Scarbrough B4G- 174.1 3,041,585 6/62 WolfeS40-174.1

IRVING L. SRAGOW, Primary Examiner.

4. APPARATUS FOR GENERATING AND RECORDING SYNCHRONIZATION PULSES ON ATRACK OF A ROTATABLE RECORD MEDIUM SAID APPARATUS COMPRISING: MEANSGENERATING ONE PULSE PER REVOLUTION OF SAID RECORD MEDIUM; MEANSUTILIZING ONE SUCH PULSE FOR BUILDING UP A CONTINOUSELY REGENERATIVECLOSED LOOP OF EQUALLY SPACED PULSES; MEANS MANUALLY ADJUSTING THEPERIOD OF THE PULSES IN SAID LOOP; MEAN COUNTING AND DISPLAYING THENUMBER OF PULSES AVAILABLE WITHIN ONE REVOLUTION OF SAID RECORD MEDIUM;AND CONTROLLABLE MEANS TRIGGERED DURING ONE REVOLUTION OF SAID RECORDMEDIUM FOR TRANSFERRING A CONTINUOUS TRAIN OF PULSES FROM SAID CLOSEDLOOP TO A TRACK ON SAID RECORD MEDIUM.